This invention relates to a dual mode suspension damper which is switched between different levels of damping by a magnetostrictive element controlled by a magnetic field.
Vehicle suspension systems require suspension dampers (such as shock absorbers or struts) to control oscillations in the vehicle suspension system. Conventional dampers include a housing filled with damping fluid and a piston slidable in the housing. A piston rod extends from the housing and connects the piston to the sprung mass (body) of the vehicle, while the housing is attached to an unsprung mass of the vehicle. Appropriate valving within the piston controls communication of damping fluid across the piston, to thereby dampen the suspension oscillations. Since conventional dampers have only a single valve in the piston and therefore are able to damp only at a set damping force, such dampers involve compromises in vehicle suspension performance.
More recently, variable suspension dampers have been proposed, in which the damping level can be varied between two separate levels in response to varying vehicle operating conditions as sensed by sensors on the vehicle. Such a damper is disclosed in U.S. Pat. No. 5,690,195. In the damper disclosed in this patent, two separate flow paths with separate valving are provided through the piston. A solenoid valve controls communication through one of the flow paths. Accordingly, damping can be adjusted or varied between two different levels, depending upon vehicle operating conditions.
According to the present invention, parallel paths are provided through the piston of a suspension damper, each of which are provided with separate damping valving. Communication through one of the paths is controlled by a movable valve element, which is controlled by a magnetostrictive element which deforms in response to application of a magnetic field. The movable valve element responds to changes in the magnetostrictive element as a result of application of a magnetic field to open or close the corresponding path. Magnetostrictive materials used to fabricate the magnetostrictive elements used in this invention include nickel and various other compounds available commercially.